Power Flat Spots

[pasotibbs]

Engines are dynamic devices. They operate over a broad range of rpm's, temp's and pressures. Not to mention fuel quality etc. Unfortunatley while the engine is a dynamic device the components it is made up of are mostly static devices. Exceptions being igntion timing and fueling. It is well documented about the tuned length of the intake, exhaust, flow and velocity of the intake and exhaust, port size, cam timing and valve lift, bore, stroke blah blah blah. At times (rpm) these static systems work well, at others they work poorly. When all of the static systems are working well together you get really good power, when only a few are working well your output is ok, and when they all are out of wack, power stinks. Finding the right combination is a very tricky matter and many people claim to have the proper solution which may produce good results, even though it can vary from another method that produces as good as results.

 

Car makers (and some mc makers) have been adding dynamic systems to the engines, multi-length intakes, variable valve timing and lift, exhaust backpressure valves, etc. Even experiments with variable compression have been done. Most of these systems are better able to perform over a broader rpm range thus minimizing the "out of wack" flat spots.

 

Engines are very simple devices that mainly are design to ingest a quantity of air, heat it up really fast, and use the expanding gas (nitrogen) to do something, move a piston, turn a rotor, spin a turbine, etc. The more air in, the hotter you get it, the more power you get out the the fuel.

 

 

Most likely the imfamous "flat spot" and resulting lean running is not just a fueling / timing issue. Otherwise a simple reprogram would solve the problem quickly. Many have reported sucess by changing the crossover and reprograming, I am sure there is dyno chart around here somewhere. Could a cylinder head re-design (proper porting) and correct cam also solve the problem. Maybe.

 

 

Do you think its possible that the flatspot was designed in to pass noise tests ?

I heard that the test is carried out at a certain road speed in 2nd gear so most makers add a flatspot to match this point in the rev range, maybe just over did it or covered the entire worlds test range with 1 big flatspot

[BrianG]

Do you think its possible that the flatspot was designed in to pass noise tests ?

I heard that the test is carried out at a certain road speed in 2nd gear so most makers add a flatspot to match this point in the rev range, maybe just over did it or covered the entire worlds test range with 1 big flatspot

 

 

I think Italian engineers are either not that devious or not that smart!

[Ryland3210]

Unfortunatly not true. TP values just report how far the throttle is open. This valve corrolates to a predicted airflow. Which may or may not be right.

 

Gee, I thought the word "sign" was general enough to survive a validity challenge!

[BrianG]

Gee, I thought the word "sign" was general enough to survive a validity challenge!

Bwaaahaaahaaa......... not around here!

[Pierre]

David, what's the source for the ignition advance chart?

[dlaing]

David, what's the source for the ignition advance chart?

The stock map from my ECU as interpreted by my Tune Boy software

I graphed the 84.56% throttle data across all the RPMs.

I spaced the spread sheet entries so that curve would show.

It is not perfectly accurate in the spacing of the bars for some reason <_>

But the curve gives a pretty good indication.

Tuneboy has 3D graphing capability, maybe I will post.

I need a new usb memory stick so I can shuttle between garage PC and internet connected Mac.

The upper row of the upper map in this image is what was graphed

[motoguzznix]

Unfortunatly not true. TP values just report how far the throttle is open. This valve corrolates to a predicted airflow. Which may or may not be right.

This is right, but only for one engine that is tuned to suit the air/fuel requierement.

 

If You change the amount of air that passes through the engine, the amount of fuel has to change too. Every change in the exhaust/intake/CR area changes airflow and thus mixture lean/richness. When there were a MAP sensor added to the system, some self adjustment would be posible.

 

Do you think its possible that the flatspot was designed in to pass noise tests ?

I heard that the test is carried out at a certain road speed in 2nd gear so most makers add a flatspot to match this point in the rev range, maybe just over did it or covered the entire worlds test range with 1 big flatspot

No, I don't think so.

Different A/F ratio in the area of the flat spot did not cure the flat spot, see my graphs posted above.

 

The stock map from my ECU as interpreted by my Tune Boy software

I graphed the 84.56% throttle data across all the RPMs.

David

 

My graph above is a good indication that the ignition timing needs to be retarded to give best power. I subtracted 3° off the figures in the upper 85deg row and got better performance in most rpm areas.

One reason might be the fact that better charge of the combustion chamber (caused by exhaust changes p.ex.) burns better and thus can work with less ignition advance. It would be worth to investigate in this area.

[emry]

Do you think its possible that the flatspot was designed in to pass noise tests ?

 

No, but some feel that the very tight valve clearences (at least here in the US) were done to help noise tests.

 

Motoguzzinix - Quite right, a MAF or other element designed to sense pressure would make for a better fueling. In our case predicted airflow was calculated by the factory and used to generate our static 3D fueling map.

[GuzziMoto]

MAF's have their own problems.Many cars use them because they are cheap and easy to pass emissions with. But cars like my Honda civic did fine without and motorcycles like my Buell which had the best fuel injection I've seen made due without. I would rather have a F.I. system without MAF's then one with. Give me a system with a quality O2 sensor, preferably wide band, that is capable of closed loop running like the Buell system.

As for the dip in the powerband, it is probably caused by intake and exhaust issues, not F.I. issues and a MAF sensor would not make a bit of difference. Remember, an engine is just a giant air pump.

[dlaing]

Do you think its possible that the flatspot was designed in to pass noise tests ?

I heard that the test is carried out at a certain road speed in 2nd gear so most makers add a flatspot to match this point in the rev range, maybe just over did it or covered the entire worlds test range with 1 big flatspot

The stock crossover appears to be the cause of the flatspot.

Guzzi could have put a simple X cross over, but they wanted something that would also help it pass noise tests, so they created the baffled stock crossover, and thus the flat spot appear to be the result.

They could have used an X-over and quieter mufflers to obtain the same sound but that would likely have reduced top end power, making it less marketable.

I suppose the flat spot in the middle allows them to run leaner and or with more advance at that point, perhaps helping pass emission testing???

[dlaing]

 

My graph above is a good indication that the ignition timing needs to be retarded to give best power. I subtracted 3° off the figures in the upper 85deg row and got better performance in most rpm areas.

One reason might be the fact that better charge of the combustion chamber (caused by exhaust changes p.ex.) burns better and thus can work with less ignition advance. It would be worth to investigate in this area.

I agree.

There is plenty of room for optimization of the timing.

Judging by the graphs there is also plenty of room to optimize the individual cylinders.

I still have to get my second hand wide band sensor working

But using your output as a guide I can at least make some changes at WOT.

Thanks!

[Guest ratchethack]

The stock crossover appears to be the cause of the flatspot.

I wouldn't agree with this, no. Not at all. The flat spot exists whether the stock crossover is installed, an aftermarket crossover is installed, or there's no crossover at all, and depends on a complex combination of many factors, most of them centered around head flow and the engine's characteristic intake and power pulse wave dynamics, which can be greatly affected by many aspects of head, valve, cam, and piston crown configuration and design. External to the heads, overall characteristics of intake and exhaust breathing contribute heavily to the shape of the curves on a dyno. Changing the crossover can improve the exhaust wave pulse harmonics on a V11 to a limited degree. But best case, taken by itself, this can only "fill in the dip" on the torque and power charts slightly at 4K - 4.5K RPM. The flat spot is still there. Many engines of all configurations have a flat spot or multiple flat spots in the torque and/or power curves, regardless of any crossover.

[dlaing]

I wouldn't agree with this, no. Not at all. The flat spot exists whether the stock crossover is installed, an aftermarket crossover is installed, or there's no crossover at all, and depends on a complex combination of many factors, most of them centered around head flow and the engine's characteristic intake and power pulse wave dynamics, which can be greatly affected by many aspects of head, valve, cam, and piston crown configuration and design. External to the heads, overall characteristics of intake and exhaust breathing contribute heavily to the shape of the curves on a dyno. Changing the crossover can improve the exhaust wave pulse harmonics on a V11 to a limited degree. But best case, taken by itself, this can only "fill in the dip" on the torque and power charts slightly at 4K - 4.5K RPM. The flat spot is still there. Many engines of all configurations have a flat spot or multiple flat spots in the torque and/or power curves, regardless of any crossover.

Yes, there are other factors, and the waves that engine generates are not caused by the exhaust but their reverberations and how they move are greatly effected by the exhaust.

But replacing the crossover gets rid of 50 to 120% of the flat spot.

FBF Stucchi and Quat-D seem to get rid of just under 100% of the dip.

Mistrals seem to get rid of more than 100% of the dip.

Re-positioning the crossover might have an even greater effect.

EDIT How much of the flat spot is removed is relative to how you define a flat spot.

To my mind if the HP is flat or downward, that is a flat spot.

Dips in the torque curve are not necessarily flat spots

After defining it that way, I can say that the FBF, Stucchi and Quat D in most cases remove that flat spot completely.

Although there is still less increase in HP through the 4000 RPM range.

[Guest ratchethack]

. . . the waves that engine generates are not caused by the exhaust but their reverberations and how they move are greatly effected by the exhaust.

[. . . sigh . . .]

[Skeeve]

Yes, there are other factors, and the waves that engine generates are not caused by the exhaust but their reverberations and how they move are greatly effected by the exhaust.

But replacing the crossover gets rid of 50 to 120% of the flat spot.

FBF Stucchi and Quat-D seem to get rid of just under 100% of the dip.

Mistrals seem to get rid of more than 100% of the dip.

 

Yeah, but: the flat spot is an artifact of the exhaust being tuned for peak #s: fill in more of the flat spot, lose more on top. What we need is a Guzzi equivalent to EXUP, ie: a tuned exhaust to get a complimentary resonance in the 4k band & then at rpms>6k, ping! the valve opens to shorten the effective header length to something that's tuned for peak power in the 7.5k rpm area.

 

Of course, it's easy to suggest the solution: putting it into practice is a little more involved...